The present invention relates to a process for preparing polyamides, which comprises polymerizing starting monomers or starting oligomers in the presence of at least one compound of the formula (I) 
where
R is a functional group R8 which bears 1-4 identical or different amide-forming groups R7,
R1 is H, C1-C20-alkyl, cycloalkyl, benzyl or OR6, where R6 is H, C1-C20-alkyl, cycloalkyl or benzyl,
R2, R3, R4 and R5 are independently C1-C10-alkyl,
n is a natural number greater than 1, and
the piperidine derivatives attached to R are identical or different with regard to the substituents, meaning R1, R2, R3, R4 and R5.
It further relates to polyamides obtainable by this process, to the use of such polyamides for preparing filaments, fibers, films, sheetlike structures and moldings, and to filaments, fibers, films, sheetlike structures and moldings comprising such a polyamide.
The preparation of polyamides, including nylon-6 and nylon-6,6, by addition or condensation polymerization from appropriate starting monomers or starting oligomers is common knowledge (Adolf Echte, Handbuch der technischen Polymerchemie, VCH Weinheim, 1993, p. 553).
The application properties of such polyamides, such as heat stability, light stability, dyeability, resistance to the washing out of color (color wetfastness), are unsatisfactory for many applications.
For instance, coloration problems can arise as a result of chemical changes (oxidative/thermal damage) to the polymer during carpet yarn or textile fabric heat setting. Both continuous filaments and staple fibers can be affected.
It is known to add stabilizers to the polyamide to improve these properties. Such an addition can take place before, during or after the polymerization, for example during the processing.
If the stabilizers are mixed into the polyamide and not attached to the polymer chain, they can migrate, evaporate or wash out of the polymer, so that the effectiveness of the stabilization decreases in an undesirable manner and the surroundings (air, dyebath, cleaning baths) may become contaminated. For instance, DE-A-39 01 717 describes improving the dyeability of polyamides by adding small amounts of at least one amino or imino compound having a cycloalkyl, aryl or hetaryl moiety in the molecule.
The addition of 2,2,6,6-tetramethylpiperidine derivatives with an amide-forming group in position 4 and with or without substitution in position 1 during the polymerization is described for example in WO 95/28443, DE-A-44 13 177, WO 97/05189 and Wo 97/13800. The use of these stabilizers leads to a reduction in the rate of polymerization and hence to higher manufacturing costs for the polyamides due to a reduced space-time yield. In addition, the wetfastness of such polyamides is unsatisfactory.
It is an object of the present invention to provide a process for preparing polyamides, polyamides obtainable by this process, the use of such polyamides for preparing filaments, fibers, films, sheetlike structures and moldings, and also filaments, fibers, films, sheetlike structures and moldings comprising such a polyamide without the disadvantages mentioned.
We have found that this object is achieved by the process for preparing polyamides defined at the beginning, polyamides obtainable by this process, the use of such polyamides for preparing filaments, fibers, films, sheetlike structures and moldings, and also filaments, fibers, films, sheetlike structures and moldings comprising such a polyamide.
Polyamides are herein to be understood as being homopolymers, copolymers, blends and grafts of synthetic long-chain polyamides having recurring amide groups in the polymer main chain as an essential constituent. Examples of such polyamides are nylon-6 (polycaprolactam), nylon-6,6 (polyhexamethyleneadipamide), nylon-4,6 (polytetramethyleneadipamide), nylon-6,10 (polyhexamethylenesebacamide), nylon-7 (polyenantholactam), nylon-11 (polyundecanolactam), nylon-12 (polydodecanolactam). As well as polyamides known by the generic name of nylon, polyamides further include the so-called aramids (aromatic polyamides), such as poly-meta-phenylene-isophthalamide (NOMEX(copyright) fiber, U.S. Pat. No. 3,287,324) or poly-para-phenylene-terephthalamide (KEVLAR(copyright) fiber, U.S. Pat. No. 3,671,542).
Polyamides can in principle be prepared by two methods.
In a polymerization from dicarboxylic acids and diamines and also in a polymerization from amino acids, the amino and carboxyl end groups of the starting monomers or starting oligomers react with one another to form an amide group and water. The water can subsequently be removed from the polymer. In a polymerization from carboxamides, the amino and amide end groups of the starting monomers or starting oligomers react with one another to form an amide group and ammonia. The ammonia can subsequently be removed from the polymer. This form of polymerization is customarily known as a condensation polymerization or polycondensation.
A polymerization from lactams as starting monomers or starting oligomers is customarily known as an addition polymerization.
Suitable starting monomers or starting oligomers for preparing polyamides are for example:
monomers or oligomers of C2 to C20, preferably C3 to C18, amino acids, such as 6-aminocaproic acid, 11-aminoundecanoic acid, and also their dimers, trimers, tetramers, pentamers or hexamers,
monomers or oligomers of C2 to C20 amino acid amides, such as 6-aminocaproamide, 11-aminoundecanoamide, and also their dimers, trimers, tetramers, pentamers or hexamers,
monomers or oligomers of a C2 to C20, preferably C2 to C12, alkyldiamine, such as tetramethylenediamine or preferably hexamethylenediamine,
with a C2 to C20, preferably C2 to C14, aliphatic dicarboxylic acid, such as sebacic acid, decanedicarboxylic acid or adipic acid,
and also dimers, trimers, tetramers, pentamers or hexamers thereof,
monomers or oligomers of a C2 to C20, preferably C2 to C12, alkyldiamine, such as tetramethylenediamine or preferably hexamethylenediamine,
with a C8 to C20, preferably C8 to C12, aromatic dicarboxylic acid or its derivatives, for example chlorides, such as 2,6-naphthalenedicarboxylic acid, preferably isophthalic acid or terephthalic acid,
and also its dimers, trimers, tetramers, pentamers or hexamers,
monomers or oligomers of a C2 to C20, preferably C2 to C12, alkyldiamine, such as tetramethylenediamine or preferably hexamethylenediamine,
with a C9 to C20, preferably C9 to C18, arylaliphatic dicarboxylic acid or its derivatives, for example chlorides, such as o-, m- or p-phenylenediacetic acid,
and also its dimers, trimers, tetramers, pentamers or hexamers,
monomers or oligomers of a C6 to C20, preferably C6 to C10, aromatic diamine, such as m- or p-phenylenediamine,
with a C2 to C20, preferably C2 to C14, aliphatic dicarboxylic acid, such as sebacic acid, decanedicarboxylic acid or adipic acid,
and also its dimers, trimers, tetramers, pentamers or hexamers,
monomers or oligomers of a C6 to C20, preferably C6 to C10, aromatic diamine, such as m- or p-phenylenediamine,
with a C8 to C20, preferably C8 to C12, aromatic dicarboxylic acid or its derivatives, for example chlorides, such as 2,6-naphthalenedicarboxylic acid, preferably isophthalic acid or terephthalic acid,
and also its dimers, trimers, tetramers, pentamers or hexamers,
monomers or oligomers of a C6 to C20, preferably C6 to C10, aromatic diamine, such as m- or p-phenylenediamine,
with a C9 to C20, preferably C9 to C18, arylaliphatic dicarboxylic acid or its derivatives, for example chlorides, such as o-, m- or p-phenylenediacetic acid,
and also its dimers, trimers, tetramers, pentamers or hexamers,
monomers or oligomers of a C7 to C20, preferably C8 to C10, arylaliphatic diamine, such as m- or p-xylylenediamine,
with a C2 to C20, preferably C2 to C14, aliphatic dicarboxylic acid, such as sebacic acid, decanedicarboxylic acid or adipic acid,
and also its dimers, trimers, tetramers, pentamers or hexamers,
monomers or oligomers of a C7 to C20, preferably C8 to C18, arylaliphatic diamine, such as m- or p-xylylenediamine,
with a C6 to C20, preferably C6 to C10, aromatic dicarboxylic acid or its derivatives, for example chlorides, such as 2,6-naphthalenedicarboxylic acid, preferably isophthalic acid or terephthalic acid,
and also its dimers, trimers, tetramers, pentamers or hexamers,
monomers or oligomers of a C7 to C20, preferably C8 to C18, arylaliphatic diamine, such as m- or p-xylylenediamine,
with a C9 to C20, preferably C9 to C18, arylaliphatic dicarboxylic acid or its derivatives, for example chlorides, such as o-, m- or p-phenylenediacetic acid,
and also its dimers, trimers, tetramers, pentamers or hexamers,
monomers or oligomers of a C2 to C20, preferably C2 to C18, arylaliphatic or preferably aliphatic lactam, such as enantholactam, undecanolactam, dodecanolactam or caprolactam,
and also homopolymers, copolymers, blends and grafts of such starting polymers or starting oligomers.
Preference is given here to those starting monomers or starting oligomers which polymerize to form the polyamides nylon-6, nylon-6,6, nylon-4,6, nylon-6,10, nylon-7, nylon-11, nylon-12 and the aramids poly(meta-phenyleneisophthalamide) or poly(paraphenyleneterephthalamide), especially nylon-6 and nylon-6,6.
In the compound of the formula (I), R is a functional group bearing 1-4 identical or different amide-forming groups R7.
R is suitably a C1 to C20, preferably C6 to C18, aromatic, preferably aliphatic unsaturated, preferably saturated, hydrocarbon R8 bearing the 1-4 amide-forming groups R7.
The hydrocarbons R8 can bear functional groups, such as ether groups, non-amide-forming amine groups or acid groups, such as phosphonic acid, phosphoric acid, preferably sulfonic acid groups or their derivatives, preferably salts, especially alkali metal salts, such as lithium, sodium or potassium salts.
In a preferred embodiment of the process of the present invention, R8 is C1-C20-alkylene, especially hexamethylene, having no further functional groups apart from R7.
The amide-forming group R7 can be selected from xe2x80x94(NHR9), where R9 is H, alkyl having from 1 to 8 carbon atoms, cycloalkyl having from 3 to 10 carbon atoms or alkylene having from 2 to 20 carbon atoms, carboxyl, a carboxyl derivative group or preferably xe2x80x94(NH)xe2x80x94. If R bears a plurality of groups R7, these groups can be different or preferably identical.
R1 is suitably alkyl having from 1 to 20, preferably from 1 to 18, carbon atoms, a substituted or preferably unsubstituted benzyl group or a group OR6, where R6 is an alkyl group having from 1 to 20, preferably from 1 to 18 carbon atoms, a substituted or preferably unsubstituted benzyl group or preferably hydrogen. R1 is particularly preferably hydrogen.
Suitable radicals R1 R3, R4 and R5 are independently alkyl having from 1 to 10 carbon atoms, preferably methyl or ethyl, especially methyl. R2, R3, R4 and R5 can be different or preferably identical.
The index n can be a natural number greater than 1, such as 2, 3, 4, 5 or 6, preferably 2, 3 or 4, especially 2.
The piperidine derivatives attached to R can be identical or different, preferably identical.
Compound (I) can be a single chemical compound or a mixture of different compounds.
A particularly preferred compound of the formula (I) is 1,6-bis-(4-amino-2,2,6,6-tetramethylpiperidino)hexane. This compound and its preparation are common knowledge and it is commercially available for example from Aldrich Chemical Company, Inc.
The compound of the formula (I) is added to the starting monomers or to the polymerizing reaction mixture and becomes attached to the polyamide through reaction of at least one of the amide-forming groups R7. The secondary amino groups of the piperidine ring systems do not react because of steric hindrance.
By chemically attaching the compound (I) to or within a polyamide, the process of the present invention provides polyamides having the advantageous properties mentioned at the beginning. The process of the present invention thus offers the advantage of obviating the separate step otherwise necessary to improve the properties of pure polyamides by admixture of compounds. This eliminates problems or quality reductions as can arise on incorporation of such compounds following surface application to the polymer granules as a result of incompatibility, viscosity degradation, migration, vaporization or washoff of these compounds or stresses as occur with compounding.
The polymerization of the starting monomers in the presence of the compound (I) is preferably carried out according to customary processes. For instance, the polymerization of caprolactam in the presence of a compound (I) can be carried out for example according to the continuous or batchwise processes described in DE-A 14 95 198, DE-A 25 58 480, DE-A 44 13 177, Polymerization Processes, Interscience, New York, 1977, p. 424-467 and Handbuch der Technischen Polymerchemie, VCH Verlagsgesellschaft, Weinheim, 1993, p. 546-554. The polymerization of 66 salt in the presence of a compound (I) can be carried out by the customary batchwise process (see: Polymerization Processes, Interscience, New York, 1977, p. 424-467, especially 444-446) or by a continuous process, for example as described in EP-A 129 196. In principle, compound (I) and the starting monomers can be introduced into the reactor separately or as a mixture. The compound (I) is preferably added according to a predetermined amount/time program.
In a preferred embodiment, the compound (I) is added to the starting monomers in an amount of from 0.015 to 0.4 mol %, preferably from 0.025 to 0.25 mol %, based on 1 mol of amide groups of the polyamide. This amount is based for example on 1 mol of caprolactam when nylon-6 is to be prepared or on 0.5 mol of 66 salt when nylon-6,6 is to be prepared.
In a preferred embodiment of the invention, the compound (I) is combined with at least one of the customary chain regulators. Examples of suitable chain regulators are aliphatic and aromatic monocarboxylic acids such as acetic acid, propionic acid and benzoic acid, aliphatic and aromatic dicarboxylic acids such as C4-C10-alkanedicarboxylic acids, preferably sebacic acid and dodecanedioic acid, especially adipic acid and azelaic acid, aliphatic C5-C8-cycloalkanedicarboxylic acids, especially cyclohexane-1,4-dicarboxylic acid, aromatic dicarboxylic acids such as benzene- and naphthalene-dicarboxylic acids, preferably isophthalic acid, 2,6-naphthalenedicarboxylic acid, especially terephthalic acid, monofunctional amines and bifunctional amines, preferably hexamethylenediamine or cyclohexyldiamine and also mixtures of such acids and mixtures of such amines. The chain regulator combination and the amounts used are selected inter alia according to the desiredpolymer properties, such as viscosity or end group content. When dicarboxylic acids are used as chain regulators, it is preferable to use the chain regulator in an amount of from 0.06 to 0.6 mol %, preferably in an amount of from 0.1 to 0.5 mol %, based on 1 mol of amide group of the polyamide.
In another preferred embodiment, the polymerization of the process of the present invention is carried out in the presence of at least one pigment. Preferred pigments are titanium dioxide, preferably titanium dioxide in the anatase form, or color-conferring compounds which are organic or inorganic in character. The pigments are preferably added in an amount of from 0 to 5 parts by weight, especially in an amount from 0.02 to 2 parts by weight, based on 100 parts by weight of polyamide. The pigments can be added to the reactor with the starting materials or separately therefrom. The use of a compound (I) (even as a chain regulator constituent) considerably improves the properties of the polymer compared with a polymer incorporating only pigment and no compound (I) or only pigment and one of the 2,2,6,6-tetramethylpiperidine derivatives mentioned at the beginning.
The polyamides of the present invention are advantageously useful for preparing filaments, fibers, films, sheetlike structures and moldings. Filaments obtained from polyamides, especially polycaprolactam, by high speed spinning at takeoff speeds of at least 4000 m/min are particularly advantageous. The filaments, fibers, films, sheetlike structures and moldings obtained using the polyamides of the present invention have many uses, for example as textile apparel or carpet fibers.